EFFECTS OF ZINC-DEFICIENCY ON CONCENTRATIONS OF LIPIDS IN LIVER AND PLASMA OF RATS

The present paper reviews the effects of zinc deficiency on concentrat ions of lipids in liver and plasma of rats. Results originate either f rom classical zinc deficiency experiments or from experiments with for ce-fed rats. Classical zinc deficiency experiments have the disadvanta ge that zinc-deficient rats largely reduce food intake, and therefore the effects of zinc deficiency on lipid metabolism are confounded by l ow food intake. This disadvantage can be overcome by force-feeding rat s sufficient quantities of a zinc-deficient diet. Experiments with for ce-fed rats have shown that the effect of zinc deficiency on concentra tions of hepatic lipids depends on the type of dietary fat. Feeding a zinc-deficient diet with predominately coconut oil causes a fatty live r characterized by largely elevated concentrations of triglycerides wi th saturated and monounsaturated fatty acids compared with control rat s. in contrast, feeding zinc-deficient diets with linseed oil or fish oil does not produce a fatty liver. Since zinc deficiency also affects the regulation of hepatic lipogenic enzymes it is probable that the f atty liver in zinc-deficient rats is due to increased lipogenesis. Add itionally, experimental data indicate that secretion of lipids from li ver into blood may be impaired by zinc deficiency. Zinc-deficient rats force-fed different types of dietary fat develop hyperlipidemia which may be a compensatory way to avoid triglyceride accumulation in the l iver. In contrast to force-fed rats, rats consuming a zinc-deficient d iet ad libitum do not gain a fatty liver. This may be due to the low f ood intake in those rats which suppresses hepatic lipogenic enzymes. T he results about the effects of zinc deficiency on concentrations of l ipids in plasma of rats fed ad libitum zinc-deficient diets are not co nsistent. However, most of the studies point to a hypolipidemia in zin c-deficient rats which is in contradiction to results in force-fed rat s.